1. Field
Aspects of the disclosure relate generally to wireless communication and more particularly, but not specifically, to opportunistic receive diversity.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is a global system for mobile communications (GSM) network. Enhanced general packet radio service (EGPRS) is an extension of GSM technology providing increased data rates beyond those available in second-generation GSM technology. EGPRS is also known as Enhanced Data rates for GSM Evolution (EDGE).
In conventional GSM wireless communication technology, different users are multiplexed by using time division multiple access (TDMA), where within one frequency channel each user is allocated resources according to a time schedule, dividing up resources among users using one time slot per user. VAMOS (Voice services over Adaptive Multi-user channels on One Slot) is an enhancement that enables doubling of the standard network capacity for voice calls. Specifically, in VAMOS, different training sequence codes are used to enable a base station to multiplex (or pair) two users onto the same resource (i.e., the same frequency and the same time slot). In addition, to facilitate sharing of the resource, lower transmit power may be allocated to each user as compared to conventional GSM.
Generally, a mobile device (e.g., a mobile station (MS), a user equipment (UE), etc.) configured for GSM uses a SIM or USIM card (subscriber identity module or universal subscriber identity module) to store the subscriber's identity and for other security and authentication purposes. Some mobile devices have multi-SIM capability, and accordingly, multiple subscriptions for wireless service. Moreover, these mobile devices may have two or more radio frequency (RF) chains (receive and/or transmit). Such devices may be referred to as dual-SIM, multi-SIM, dual-SIM dual-standby (DSDS), dual-SIM dual active (DSDA), tri-SIM dual active (TSDA), and so on. For some deployments, a mobile device vendor may compromise the RF quality of a mobile device to reduce costs. For example, a low cost mobile device may include a less sensitive RF receive chain.
The use of a low sensitivity receive chain may cause performance issues in mobile devices that use VAMOS. If two or more mobile devices share same VAMOS channel, the signals from the mobile devices will interfere on the VAMOS channel. For example, when the subchannel power imbalance ratio (SCPIR) is 0 dB, a VAMOS channel may experience 3 dB less power (as compared to conventional GSM) due to peak to average effect in the VAMOS channel. Thus, there is a need for improved performance in mobile devices that support VAMOS.